(a) Field of the Invention
The invention relates to a color correction method, particularly to a color correction method for a display apparatus and a color correction apparatus thereof.
(b) Description of the Related Art
Accompanying with the advance of technology, commercial display apparatuses are diversified, commonly seen like a CRT TV, a liquid crystal display, a plasma TV, and a back projection TV. Since the image displaying principle for each apparatus is different, the color presentation is different. Thus, how to promote the color reproduction efficiency of a display apparatus is an important task. The signal processing for image color reproduction of a display apparatus comprises the following two major subjects.
At first, each display apparatus has its own color displaying characteristic and the color coordinates of a RGB three-primary color image shown by the display apparatus in a color space comprise a specific color gamut. In order to have the image signal inputted by each display apparatus be displayed with correct and consistent colors, the color displaying characteristic of each display apparatus should be complied and the color gamut mapping method should be utilized to have the color appearance of the image displayed by each display apparatus be the same.
Secondly, the image signal transmitted to the display apparatus has a non-linear relation between the gray level and the signal intensity thereof. Such a relation is called “gamma characteristic”. The gamma characteristic can be represented by a function with a non-linear curve. As the inputted image pixel datum signal is “x”, the luminance of the pixel is represented by xγ, where γ is a gamma exponent that changes with the corresponding specification of the image signal. In order to have the linear relation between the reproduced image pixel and the intensity of the original image signal, the display apparatus needs an image processing unit to perform Gamma correction for the image signal. Generally, there are two types of gamma correction methods. One method is to use digital signal processing (DSP) to calculate the gray level corresponding to the input value by the gray function. One method is to use a look-up table to obtain the gray level corresponding to the input value. The look-up table records the calculated gray level before and after conversion and is built in firmware or hardware. When performing gamma correction, the input value is used to find out the corresponding output value.
Please refer to FIG. 1 that is a schematic diagram illustrating the system configuration of a display apparatus 1 according to the prior art. As shown in FIG. 1, an image source S inputs an image signal to the display apparatus 1. The image signal is processed by an image processing unit 10 and then outputted to a panel 16 for displaying. The image processing unit 10 comprises a Gamma converting module 12 and a color gamut mapping module 14. The Gamma converting module 12 is to perform Gamma conversion for the image signal and the color gamut mapping module 14 is to perform color gamut mapping for the image signal. The needed parameters for the Gamma converting module 12 and the color gamut mapping module 14 to perform Gamma conversion and color gamut mapping, respectively, are set by a color correction process after the display apparatus 1 is assembled.
In the prior technique, the color correction process includes the steps of displaying a full-white image on the panel 16 of the display apparatus 1, measuring the chromatic value and the luminance to obtain the Gamma characteristic and the color gamut of the display apparatus 1, setting the parameters for the Gamma converting module and the color gamut according to the measured chromatic value and luminance value. After the parameters are set, the display apparatus 1 is again driven to display the full-white image on the panel 16 and the chromatic value and the luminance of the full-white image are measured to confirm that a target color temperature range is achieved. If the target color temperature range is achieved, the parameter setting for the display apparatus 1 is completed. If not, the parameter setting for the display apparatus 1 is continued until the target color temperature, range is achieved. However, this color correction process is to perform non-linear RGB gain adjustment based solely on the full-white image and thus only the full-white image can reach the target color temperature range while the image with the rest of the gray level can not.